Fluorescent lamp or similar device containing an amalgam of tin-indium-mercury which controls the mercury vapor pressure during operation



Sept. 1, 1970 G FLUORESCENT LAMP OR S. EVANS ETAL SIMILAR DEVICE CONTAINING AN AMALGAM OF TIN-INDIUM-MERCURY WHICH CONTROLS THE MERCURY Filed Oct. 2'7. 1967 VAPOR PRESSURE DURING OPERATION 2 Sheets-Sheet l George S Evans and Chalmers Moreheod AGE Sept. 1, 1970 Filed Oct. 27, 1967 G. S- EVANS ETAL FLUORESCENT LAMP OR SIMILAR DEVICE CONTAINING AN AMALGAM OF TIN-INDIUM-MERGURY WHICH CONTROLS THE MERCURY VAPOR PRESSURE DURING OPERATION 2 Sheets-Sheet 2.

PERCENT WAT TS VOLTS AMPERES (0)RELAT|VE LIGHT OUTPUT AMBIENT TEMPERATURE (F) 38(4Sn-83 In I3 Hg) AMBIENT TEMPERATURE (F) (b) LAMP WATTS (c) LAMP VOLTS AMBIENT TEMPERATURE(F) (d LAMP CURRENT AMBIENT TEMPERATURE (F) FIG.3

United States Patent O FLUORESCENT LAMP OR SIMILAR DEVICE CON- TAINING AN AMALGAM OF TIN-INDIUM-MER- CURY WHICH CONTROLS THE MERCURY VA- POR PRESSURE DURING OPERATION George S. Evans, Caldwell, and Chalmers Morehead, Upper Montclair, N.J., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 27, 1967, Ser. No. 678,702 Int. Cl. H01j 19/70 U.S. Cl. 3-13-174 5 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATIONS The present application is related to the following copending applications:

Ser. No. 381,503 filed July 9, 1964 by George S. Evans and entitled Mercury Vapor Discharge Lamp And Pressure Regulating Means Therefor; and

Ser. No. 524,898 filed Feb. 3, 1966 by George S. Evans and entitled Fluorescent Lamp Having An Integral Mercury-Vapor Pressure Control Assembly With Seg-.

mented Amalgam-Forming Metal.

Both of the aforesaid applications are assigned to the assignee of the present application. Application Ser. No. 524,898 discloses and claims a fluorescent lamp having a foraminous assembly which retains discrete segments of a suitable amalgam, such as a tin-indium-mercury amalgam, at a predetermined location within the lamp. Application Ser. No. 381,503 discloses and claims a mercurydischarge lamp having an indium-mercury amalgam and various types of foraminous holders.

BACKGROUND OF THE INVENTION This invention relates to mercury vapor discharge lamps and has particular reference to an improved fluorescent lamp having a mercury-vapor pressure regulating means that permits the lamp to be operated efliciently at high power loadings or within a wide range of ambient temperatures, or a combination of these conditions.

As is well known, the light output and efliciency of a fluorescent lamp reaches a maximum when the mercury vapor pressure within the lamp is maintained within the range of approximately 6 to 10 microns. This is due to the fact that the amount of 2537 a radiation produced by the discharge is at a maximum at such vapor pressures. Vapor pressures of from about 3 to 14 microns maintain the light output within 90% of peak output and are thus commercially acceptable. In fluorescent lamps of conventional loading the design parameters are so correlated that the required mercury vapor pressure is achieved under normal operating conditions. However, when the lamp is operated at high power loadings (that is, in excess of conventional loadings of about 10 watts per foot of lamp length) or high ambient temperature conditions, the mercury vapor pressure increases and the light output drops off sharply.

Fluorescent lamps have been developed and are being marketed wherein the aforesaid problem is overcome by utilizing an amalgam of indium and mercury which, by virtue of its composition and strategic location within the lamp, regulates and maintains the mercury vapor pressure Within the proper limits over a wide range of lamp operating temperatures. Such an indium-mercury amalgam and improved fluorescent lamp are disclosed in the aforementioned application Ser. No. 381,503 of George S. Evans.

While the use of indium-mercury amalgams, and particularly the amalgam compositions disclosed in the aforementioned Evans application Ser. No. 381,503, markedly improves the light output and efficiency of a fluorescent lamp under high-ambient temperature conditions or high power loadings, additional improvements in the performance of such lamps are always desirable. In addition, experience has shown that manufacturing problems are sometimes encountered in making the wire mesh amalgam-containing collars of the type described in the aforesaid Evans application Ser. No. 381,503 in which ribbons of pure indium are used. Indium is very soft and ductile and the indium ribbons tend to tear during the assembly operation.

It would accordingly be advantageous to provide an amalgamating material that is stronger than pure indium and thus can be readily and efficiently assembled with wire-mesh members to form pressure-regulating components on a mass production basis.

SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide a fluorescent lamp, or other low-pressure mercury-vapor discharge device, which contains a mercury-vapor pressure regulating component that can be easily fabricated and contains an amalgam that is equivalent to or better than indium-mercury amalgams as regards pressure control over a wide range of operating temperatures.

The aforementioned objects and other advantages are achieved in accordance with the present invention by utilizing a triple-component amalgam composed of predetermined amounts of tin, indium and mercury, in which the tin constitutes a minor constituent. According to a preferred embodiment the amalgam contains (on an atom percent basis) from about 2% to 9% tin, from about 71 to 91% indium, and from about 7 to 20% mercury; and the amounts of the various constituents are so correlated that the amalgam is in a liquid solid (two phase) state at the temperatures which prevail within the lamp when the latter is operated at high power loadings or high ambient temperatures, or both. Such amalgams have a more constant vapor pressure characteristic than does a two phase indium-mercury amalgam and thus provide a more stabilized light output over a wide range of operating temperatures. In addition, it has been found that the primary alloy of tin and indium used to form the amalgam in the finished lamp has a higher tensile strength than does pure indium. Ribbons of tin-indium alloy are thus easier to handle and facilitate the manufacture of the pressure-regulating components and lamps.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention will be obtained by referring to the drawing, wherein:

FIG. 1 is an elevational view, partly in section, of a fluorescent lamp embodying the novel mercury-vapor pressure regulating amalgam of the present invention;

FIG. 2 is a graph comparing the pressure-temperature 3 characteristic of the triple-component amalgams of the present invention with pure mercury and a two phase indium-mercury amalgam; and,

FIGS. 3(a) to (d) are graphs in which the light output, wattage, voltage, and current characteristics of a 96 inch highly-loaded fluorescent lamp containing a twophase indium-mercury amalgam are compared with those of an identical lamp containing a two-phase tin-indiummercury amalgam according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a highly-loaded fluorescent lamp consisting of a tubular glass envelope 12 that is interiorly coated with a layer 14 of a suitable ultravioletresponsive phosphor and is hermetically sealed at each end by a glass stem 16. A pair of lead wires 18 sealed through each of the stems 16 connect the cathodes 20 to pin contacts 22 that are anchored in suitable base members 24 attached to the respective ends of the envelope. The cathodes 20 comprise tungsten wire coils that are coated with electron-emissive material and are disposed between enlarged metal anodes 26 fastened to the inner ends of the lead wires 18.

The mercury-vapor pressure control component 28 consists of a wire mesh collar 29 that contains a predetermined amount of amalgam and is held in encircling relationship with the stem tube 16 by a ring clip 30. The core of amalgamating material and the overlying strips of wire mesh are assembled in the form of a collar which is then slipped over the stem 16 in accordance with the teachings of the aforementioned copending Evans application Ser. No. 381,503. As initially formed the collar 29 contains the primary amalgamating alloy only. This alloy subsequently combines with the mercury vapor within the finished lamp, when the latter is first lighted and de-energized, and forms the amalgam which thereafter controls the mercury-vapor pressure in the lamp when it is operating.

In accordance with this invention the primary amalgamating material comprises an alloy of indium and tin in amounts such that the amalgam ultimately formed with the mercury within the finished lamp contains predetermined amounts of these three metals. The proportions of the constituents comprising the amalgam are quite critical and it has been discovered that tin *must be present in only a minor amount if proper regulation is to be achieved. The permissible and preferred ranges of the various constituents in both atomic and weight percentages are given in Table I below.

Optimum results are obtained if the amalgam is in a liquid-solid or so-called two phase state at the various temperatures which prevail within the lamp during op eration. These temperatures range from about 45 C. to 90 C. in the case of so-called highly-loaded fluorescent lamps and standard 40 watt fluorescent lamps and can extend up to about 130 C., as disclosed in the aforementioned application Ser. No. 381,503 of George S. Evans. Experience has shown that the best combination of primary alloy strength and amalgam operation is achieved when the tin content is maintained between about 2 atom percent and 9 atom percent. Hence, the tin content is preferably maintained within this range, as indicated in Table I. Amalgams containing the preferred amount of tin, from 7 to 20 atom percent mercury, and the balance indium will be in a two phase state when the lamp operating temperature is within the aforesaid range of from about 45 C. to 130 C. Amalgams containing the preferred ranges of tin, indium and mercury set forth in Table I will, accordingly, provide optimum mercury-vapor pressure control at such operating temperatures.

The marked improvement in the vapor pressure regulating characteristic of the amalgam when thetin content is maintained within the aforementioned preferred range is shown in the graph depicted in FIG. 2. In this figure the vapor pressure-temperature characteristics of various amalgams are compared with that of pure mercury. Curve 32 shows pure mercury and provides vapor pressure of slightly over 4 microns at 35 C. and that the vapor pressures increases rapidly to approximately 12.7 microns at about 50 C. In contrast, curve 33 shows that a two-phase indium-mercury amalgam of the type disclosed in the above-mentioned copending Evans application (wherein indium comprises from to atomic percent of the amalgam) provides a mercury vapor pressure that increases from slightly more than 1 micron at 50 C. to approximately 2 microns at 60 C.

and finally to around 10 microns at 90 C. Hence, a twophase indium-mercury amalgam of the proper composition provides the desired mercury-vapor pressure regulation at the higher range of temperatures which prevai within highly-loaded fluorescent lamps, and is most effective at operating temperatures of from 70 C. to 90 C.

As is shown by curve 34, a triple-component amal gam embodying the present invention and containing 20 atom percent tin, 65 atom percent indium and 15 atom percent mercury provides a mercury vapor pressure that is closer to the optimum range of 6 to 10 microns at lower operating temperature than does the indium-mercury amalgam. This is apparent from the fact that approximately 2.3 microns vapor pressure is provided by this particular triple-component amalgam at 60 C. and approximately 10 microns at around 80 C. Hence, the mercury vapor pressure in a lamp containing such a triple-component amalgam will be higher at amalgamoperating temperatures of from 60 to 80 C. than in the case of an identical lamp containing a two-phase indium-mercury amalgam. Since the mercury vapor pressure is closer to the optimum 6 to 10 micron range, the lamp containing this particular triple-component amalgam will have a proportionately higher light output than an In-Hg amalgam lamp in the aforesaid operating temperature range of 60 C. to 80 C.

As is indicated in FIG. 2, a triple component amalgam consisting of 5 atom percent tin, 75 atom percent indium and 20 atom percent mercury provides mercury-vapor pressure regulation that is more favorable than the regulation provided by either the two phase In-Hg amalgam or the 20 Sn-65 In-15 Hg amalgam. This is evident from curve 35 which shows that with a tin content of 5 atom percent the vapor pressure increases from about 2.3 microns at 55 C. to approximately 4.5 microns at 62 C., and then increases at much slower rate to about 10 microns at approximately 88 C. That is, the curve has approximately the same slope as that of the indiummercury system up to about 62, at which point a sharp break occurs and the slope of the curve decreases. Hence, this particular triple-component amalgam not only has a pressure-temperature characteristic which is tailored to the operating temperature requirements of highlyloaded fluorescent lamps but has, in addition, a mercury vapor pressue characteristic that is less responsive or sensitive to changes in operating temperature. Hence, the mercury vapor pressure and the light output of a lamp containing this type amalgam will remain more constant as the ambient and operating temperatures change in comparison to an identical lamp having an amalgamating material consisting of indium. Expressed differently, the light output versus ambient temperature curve will be flatter in the case of a two-phase Sn-In-Hg amalgam lamp than for a two-phase .ln-Hg amalgam lamp, other factors being equal.

The aforementioned improvement as regards a more constant or stable light output with varying temperature is illustrated in the family of curves shown in FIGS. 3(a) through (d) comparing the operating characteristics a 96" T12 high-output fluorescent lamp that contained a two-phase In-Hg amalgam and an identical lamp that contained 4 atomic percent Sn, 83 atomic percent In, and 13 atomic percent Hg (that is, a two-phase Sn-In- Hg amalgam). As shown by curve 36 in FIG. 3(a), the light output of the lamp containing the Sn-In-Hg amalgam was much higher in the 50 F. ambient temperature region as compared to the In-Hg amalgam lamp (curve 37), and the differential gradually decreased as both lamps reached peak light output at approximately 95 F. The light output-ambient temperature curve is thus much flatter for the triple-component amalgam lamp than it is for the indium-mercury amalgam lamp.

This is verified by the wattage-ambient temperature curves for the respective lamps shown in FIG. 3(b) which show that the wattage is higher and more constant in the case of the triple-component amalgam lamp (curve 38) than in the case of the indium-mercury amalgam lamp (curve 39). The volt-ambient temperature characteristics shown in FIG. 3(c) indicates that the voltage of the triple-component amalgam lamp (curve 40) is higher at lower ambient temperatures and slightly lower at higher ambient temperatures than that of the indium-mercury lamp (curve 41).

The reverse is true for the current-ambient temperature characteristic shown in FIG. 3(d) wherein curve 42 shows that the lamp current in the case of the Sn-In- Hg amalgam lamp is slightly lower at lower temperatures than that of the In-Hg lamp (curve 43), and then increases to a slightly higher value at higher ambient temperatures. The variations in the lamp volts and current, together with the apparent lamp power factor, are such that the watts and light output for the Sn-In-Hg lamp are higher than those of the In-Hg lamp in the lower range of ambient temperatures, thus providing a lamp that has a more stabilized wattage and light output.

Comparative tests have shown that tin-indium alloys containing from 5% to 20% by weight tin have approximately twice the tensile strength of ribbons made from pure indium. This increased mechanical strength permits ribbons of primary tin-indium alloys to be readily assembled with wire mesh strips or the like and enables mesh-type amalgam-holding collars to be efficiently manufactured on a mass production basis.

ADDITIONAL SPECIFIC EXAMPLES A two-phase Sn-In-Hg amalgam suitable for a 48 inch T12 1500 ma. fluorescent lamp can be obtained by placing 115 milligrams of a primary Sn-In alloy (5% by weight Sn and 95% by weight In) in the wire mesh collar, and then dosing the lamp with about 50 milligrams of mercury in the usual fashion.

In the case of a 72 inch T12 1500 ma. lamp about 172 milligrams of the aforesaid primary Sn-In alloy can be used with 75 milligrams of mercury. The corresponding data for a 96 inch T12 1500 Ina. lamp are 230 mg. of Sn-In alloy and 100 mg. of Hg.

It will be appreciated from the foregoing that the objects of the present invention have been achieved in that a fluorescent lamp has been provided which contains an amalgam consisting of preselected amounts of tin, indium and mercury which not only enhances the performance of the lamp but makes it easier to manufacture. While several embodiments have been illustrated and described, it will be obvious to those skilled in the art that various changes in the amalgam-retaining structure and the amalgam composition can be made without departing from the spirit and scope of the invention. For example, the amalgam can be retained in the desired position within the lamp by means other than a wire mesh collar, as by attaching a body of the amalgam to the bulb wall, lead wires or stem tube with a suitable holder, etc.

In addition, the invention is not limited to fluorescent lamps but may be used in various types of mercury-vapor discharge devices, such as ultraviolet-generating lamps for example, which will exhibit an enhanced output if the mercury vapor pressure is properly controlled.

We claim:

1. In combination with a low-pressure mercury-vapor discharge lamp that contains a predetermined amount of mercury,

means for controlling the mercury-vapor pressure within said lamp during the operation thereof comprising a predetermined amount of a tin-indium alloy located in a region within said lamp such that said alloy combines with substantially all of the mercury when the lamp is de-energized and forms a tinindium-mercury amalgam that contains from about 5 to 30 atom percent mercury, from about 45 to 93 atom percent indium, and from about 2 to 25 atom percent tin.

2. The combination set forth in claim 1 wherein said amalgam contains about 15 atom percent mercury, about 20 atom percent tin and about atom percent indium.

3. The combination set forth in claim 1 wherein said lamp comprises a fluorescent lamp and said amalgam contains from about 7 atom percent to about 20 atom percent mercury, from about 2 atom percent to about 9 atom percent tin, and from about 71 atom percent to about 91 atom percent indium.

4. The combination set forth in claim 3 wherein said amalgam contains about 20 atom percent mercury, about 5 atom percent tin, and about 75 atom percent indium.

5. The combination set forth in claim 3 wherein said amalgam contains about 13 atom percent mercury, about 4 atom percent tin, and about 83 atom percent indium.

References Cited UNITED STATES PATENTS 3,152,278 10/1964 Dziergwa et al. 3l3109 X 3,263,111 7/1966 Doering 3l3-181 X 3,392,298 7/1968 Menelly 313l78 X RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 313-109, 178 

